Algebraic expressions

The expression has value 9 when x=3. Substituting gives \(k(3)^2-4(3)-6=9\), or \(9k-12-6=9\). Thus, \(9k-18=9\), so \(9k=27\) and \(k=3\). For example, if k=1, the expression does not evaluate to 9. Exam tip: Substitute the given value of the variable carefully into every term of the expression.

Like terms have exactly the same variables and powers. In the first option, every term has variable part (p^2q^3).

The governing concept is subtraction of algebraic expressions: when a complete bracket is subtracted, the sign of every term inside that bracket changes. Thus, 3a² − 2ab + 5b² − (2a² + ab − 4b²) becomes 3a² − 2ab + 5b² − 2a² − ab + 4b². Now combine like terms separately: 3a² − 2a² = a², −2ab − ab = −3ab, and 5b² + 4b² = 9b². Therefore the simplified expression is a² − 3ab + 9b², so option C is correct. Option A misses one negative ab term, option B mishandles the a² terms, and option D combines the b² terms incorrectly.

Given \(a+b=8\) and \(ab=12\), substitute these values into \(4(a+b)-ab\): \(4\times 8-12=32-12=20\). Hence, the correct answer is 20. The value 32 is only \(4(a+b)\); subtracting \(ab\) is still necessary. Exam tip: substitute the given combined expressions such as \(a+b\) and \(ab\) directly.

Apply the distributive property: \(4r(r-1)=4r^2-4r\). Also, \(-3r(2-r)=-6r+3r^2\), since \(-3r\times(-r)=+3r^2\). Combining like terms gives \(4r^2+3r^2-4r-6r=7r^2-10r\). Therefore, option A is correct. In option C, the linear terms have been combined incorrectly. Exam tip: when expanding an expression with a negative sign, check the sign of every product separately.

Combining like terms gives \(8p^2q-5p^2q=3p^2q\) and \(-3pq+6pq=3pq\). Thus, the simplified expression is \(3p^2q+3pq+4\), which has 3 terms: \(3p^2q\), \(3pq\), and \(4\). Choosing 2 would be incorrect because the constant \(4\) is also a separate term. Exam tip: Combine only terms with exactly the same variables and exponents.

In u^3v^2, the exponent of u is 3 and the exponent of v is 2, so option B is correct. In option A, the exponents are reversed: u has exponent 2 and v has exponent 3. Exam tip: read the exponent written on each variable separately.

Substituting the given values, \(x^2y=(-3)^2\times2=9\times2=18\) and \(xy^2=(-3)\times2^2=(-3)\times4=-12\). Hence, \(x^2y+xy^2=18+(-12)=6\). The distractor \(-6\) may result from handling the sign of the negative term incorrectly. Exam tip: write a negative number in brackets before squaring it; \((-3)^2=9\).

While adding polynomials, combine only like terms: \(7x^2+(-3x^2)=4x^2\), \(-4x+8x=4x\), and \(9+(-2)=7\). Therefore, the sum is \(4x^2+4x+7\). Option C incorrectly adds the linear terms. Exam tip: group terms with the same power of the variable before adding.

Given \(5x-3=22\), add 3 to both sides to get \(5x=25\), so \(x=5\). Now substitute in the expression: \(x^2+2x=5^2+2(5)=25+10=35\). Hence, 35 is the correct answer. The value 30 may result from incorrectly evaluating \(x^2\). Exam tip: first find the value of the variable from the equation, then substitute it carefully into the expression.

Like terms have exactly the same variables raised to the same powers; only their coefficients may differ. In \(-3m^2n^4\), the variable part is \(m^2n^4\), so it is a like term of \(8m^2n^4\). In \(5m^4n^2\), the powers of \(m\) and \(n\) are different, so it is not a like term. Exam tip: Ignore the coefficients and compare the variables and their exponents.

A minus sign precedes the second bracket, so the sign of every term inside it changes: \(6x^2-4xy+y^2-2x^2-5xy+3y^2\). Combining like terms gives \((6-2)x^2=4x^2\), \((-4-5)xy=-9xy\), and \((1+3)y^2=4y^2\). Hence, the simplified expression is \(4x^2-9xy+4y^2\). In option D, the sign of the \(y^2\) term is incorrect. Exam tip: when subtracting a bracket, change the sign of every term in that bracket before combining like terms.

Add the two given equations:

a-b+a+b=7+17.

The terms involving b cancel, so

2a=24.

Hence,

a=12.

Option 10 may result from incorrectly treating the result of subtracting the equations as a; subtraction actually gives 2b. Exam tip: add equations when a variable has opposite signs so that it cancels out.

The term containing x^2 is -7x^2. The numerical factor multiplying the variable part is called its coefficient, so the coefficient of x^2 is -7. Here, 4, 2, and -11 belong respectively to the x^3 term, the x term, and the constant term. Exam tip: identify the term with the required power first, then write its numerical coefficient.

Expanding the expression gives \(2(5x+3y)-7(x-y)+4x=10x+6y-7x+7y+4x\). Combining the \(x\)-terms, \(10x-7x+4x=7x\). Therefore, the coefficient of \(x\) is \(7\). The distractor \(11\) can result from mishandling the negative sign in \(-7(x-y)\). Exam tip: when a negative sign is outside parentheses, distribute it to every term inside.

In \(x^3y^4\), the powers of \(x\) and \(y\) are 3 and 4 respectively. Therefore, its total degree is \(3+4=7\), so option A is correct. \(x^2y^4\) has total degree 6; similarly, \(x^5y\) and \(xy^5\) also have total degree 6. Exam tip: for a multivariable monomial, add the exponents of all variables to find its total degree.

In a polynomial, every exponent of \(x\) must be a non-negative integer. In \(7x^4-3x+2\), the highest exponent is 4, so it is a polynomial of degree 4. Option B has highest exponent 5. Option C contains \(\sqrt{x}=x^{1/2}\), and option D contains an \(x^{-1}\) term, so neither is a polynomial. Exam tip: first check that all exponents are non-negative integers, then use the highest exponent to find the degree.

Only like terms can be combined. The terms \(9u^2v\) and \(3u^2v\) are like terms, so their sum is \(12u^2v\). Similarly, \(-5uv+8uv=3uv\), while the constant term \(-10\) remains unchanged. Therefore, the simplified expression is \(12u^2v+3uv-10\). In option A, the coefficients of the \(uv\) terms have been combined incorrectly. Exam tip: before combining terms, check that both the variables and their powers are exactly the same.

On substituting \(x=-4\), \(x^3=(-4)^3=-64\) and \(x^2=(-4)^2=16\). Hence the numerator is \(-64-2(16)+8=-64-32+8=-88\). Therefore, \(\frac{-88}{-4}=22\), so option B is correct. A value such as \(26\) can result from mishandling the negative sign in \(-2x^2\). Exam tip: the square of a negative number is positive, whereas its cube is negative.

Combine like terms while adding: \(3x^2-x^2=2x^2\), \(-2x+6x=4x\), and \(5-9=-4\). Hence, the resulting expression is \(2x^2+4x-4\). In option D, the coefficients of the \(x^2\) terms have been added incorrectly. Exam tip: add the \(x^2\), \(x\), and constant terms separately.