If (r=-2), what is the value of (r^3-4r^2+6r)?
Answer and explanation
Correct answer: -36
Substitute r=-2: r^3=(-2)^3=-8 and r^2=(-2)^2=4. Therefore, r^3-4r^2+6r=-8-4(4)+6(-2)=-8-16-12=-36. Hence, option C is correct. A common error is taking r^2 as -4, but the square of a negative number is positive. Exam tip: use brackets while evaluating powers after substitution.
Frequently asked questions
What is the correct answer to this question?
-36
Why is this the correct answer?
Substitute r=-2: r^3=(-2)^3=-8 and r^2=(-2)^2=4. Therefore, r^3-4r^2+6r=-8-4(4)+6(-2)=-8-16-12=-36. Hence, option C is correct. A common error is taking r^2 as -4, but the square of a negative number is positive. Exam tip: use brackets while evaluating powers after substitution.
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Introduction to Polynomials. Topic: Algebraic expressions.
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