What is the complete factorisation of (12x^2-27y^2)?
First take (3) common and split (4x^2-9y^2) by difference of squares. Exam tip: fully factorise the final answer.
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SubjectsMathematics
TOPIC PRACTICE
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First take (3) common and split (4x^2-9y^2) by difference of squares. Exam tip: fully factorise the final answer.
View question details\((3p+2q)^2=9p^2+2\cdot3p\cdot2q+4q^2=9p^2+12pq+4q^2\), so A is a perfect square. In B, the last term should be \(4q^2\), not \(5q^2\). Exam tip: compare the middle term with \(2ab\).
View question details(x^4-81=(x^2-9)(x^2+9)) and (x^2-9=(x-3)(x+3)). Exam tip: check difference of squares repeatedly.
View question detailsThe first three terms satisfy \(x^2-2xy+y^2=(x-y)^2\). Hence the expression is \((x-y)^2-25=(x-y)^2-5^2\). Applying \(a^2-b^2=(a-b)(a+b)\) gives \((x-y-5)(x-y+5)\). Option B would involve \((x+y)^2\), whose middle term is \(+2xy\), whereas the given expression has \(-2xy\). Exam tip: identify the perfect-square trinomial before applying the difference-of-squares identity.
View question detailsThis matches \(u^2-2uv+v^2\). With \(u=7a\) and \(v=6b\), the middle term is \(-2uv=-84ab\), so the area is \((7a-6b)^2\). Since \(7a>6b\), the positive side is \(7a-6b\). In exams, verify the middle term first.
View question detailsWe have \(9p^2=(3p)^2\) and \(16q^2=(4q)^2\). For a perfect-square trinomial, the middle term must be \(\pm2ab\). Here, \(2\times3p\times4q=24pq\), and the middle term is \(-24pq\). Therefore, \(9p^2-24pq+16q^2=(3p-4q)^2\), so option A is correct. In option B, the middle term is \(-20pq\), not the required \(-24pq\). Exam tip: take the square roots of the first and last terms, then check twice their product against the middle term.
View question details((3x-4)(2x+3)=6x^2+9x-8x-12). The middle term becomes (x), so signs must be checked carefully.
View question details\(4m^2+25n^2=(2m)^2+(5n)^2\) is a sum of squares, not a difference. The identity is \(a^2-b^2=(a-b)(a+b)\). In exams, check the sign between the two square terms first.
View question detailsFirst take (x) common and factor (x^2+3x+2) as ((x+1)(x+2)). Exam tip: factor the trinomial after common factor.
View question detailsUse \((a-b)^2=a^2-2ab+b^2\). With \(a=3p\) and \(b=4q\), the middle term is \(-2\times3p\times4q=-24pq\), and the last term is \(16q^2\). Hence A is correct. Exam tip: always check the middle-term sign.
View question detailsIn \(x^3-9x\), \(x\) is the common factor, so \(x^3-9x=x(x^2-9)\). Now \(x^2-9=x^2-3^2\) is a difference of squares; hence \(x^2-9=(x-3)(x+3)\). Therefore, the complete factorisation is \(x(x-3)(x+3)\). Option B is incorrect because \((x-3)^2\) would introduce a \(-6x^2\) term on expansion. Exam tip: take out the common factor first, then look for a difference of squares.
View question detailsIn option A, \(p^2-10p+25=(p-5)^2\) and \(49q^2=(7q)^2\), so it is a difference of two squares. Option B is a sum of squares. Exam tip: identify perfect squares first.
View question detailsHere \(16x^2=(4x)^2\) and \(9y^2=(3y)^2\). The middle term is \(-24xy=-2(4x)(3y)\), so the expression is \((4x-3y)^2\). In exams, verify the middle term against \(\pm2ab\).
View question detailsUsing \((a-b)^3=a^3-3a^2b+3ab^2-b^3\), put \(a=2x\) and \(b=3y\). This gives option A, \((2x-3y)^3\). Option C has the wrong sign for the last term. Exam tip: check the first and last terms first.
View question detailsGroup the terms as \(ab-ac+db-dc=a(b-c)+d(b-c)\). Since \((b-c)\) is common to both groups, taking it out gives \((a+d)(b-c)\). In option C, \((b+c)\) would make the \(ac\) and \(dc\) terms positive, so it is incorrect. Exam tip: Check the signs of every term carefully while grouping.
View question detailsSplit the middle term as \(15x+4x\): \(3x(2x+5)+2(2x+5)=(3x+2)(2x+5)\). Hence A is correct. Option B gives a middle term of \(16x\). Exam tip: multiply the factors to verify the middle term.
View question details\(25p^2-49q^2=(5p)^2-(7q)^2\), so it is a difference of squares and factors as \((5p-7q)(5p+7q)\). B has a sum, while C is a perfect square. Exam tip: check for two squares joined by a minus sign.
View question detailsIn option A, \(49x^2=(7x)^2\), so it has the form \((7x)^2-(3y+2)^2\), a difference of squares. Hence its factors are \((7x-3y-2)(7x+3y+2)\). Exam tip: first identify whether both terms are perfect squares with a minus sign.
View question details\(x^3-8y^3=x^3-(2y)^3=(x-2y)(x^2+2xy+4y^2)\), so \(x-2y\) is a factor. In \(x^3+8y^3\), the factor is \(x+2y\). Exam tip: identify the difference-of-cubes pattern first.
View question detailsFor \(x^2+x-1\), the discriminant is \(b^2-4ac=1+4=5\), which is not a perfect square. Hence it has no linear factors with integer coefficients. In A, 2 and 3 multiply to 6 and add to 5. Exam tip: check the discriminant first.
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