If (x+1) is a factor of the polynomial P(x)=2x^3+kx^2-5x+2, what is the value of k?
Answer and explanation
Correct answer: −5
By the Factor Theorem, if (x+1) is a factor of P(x), then P(-1)=0. Thus, P(-1)=2(-1)^3+k(-1)^2-5(-1)+2=-2+k+5+2=k+5. Hence, k+5=0, giving k=-5. Exam tip: for a factor of the form (x-a), substitute x=a; therefore, (x+1)=(x-(-1)) requires substituting x=-1.
Frequently asked questions
What is the correct answer to this question?
−5
Why is this the correct answer?
By the Factor Theorem, if (x+1) is a factor of P(x), then P(-1)=0. Thus, P(-1)=2(-1)^3+k(-1)^2-5(-1)+2=-2+k+5+2=k+5. Hence, k+5=0, giving k=-5. Exam tip: for a factor of the form (x-a), substitute x=a; therefore, (x+1)=(x-(-1)) requires substituting x=-1.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Polynomials. Topic: Polynomials in one variable.
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