Question

2x^2 +bx−10=0, if one of its roots is 5

find x and b

Answer 1

x = -1, or x = 5

b = -8

Explanation:

2x^2 +bx−10=0 (1)

If one of the x value is 5, then:

2×(5)^2 + b×5 - 10 = 0

<=> 50 + 5×b - 10 = 0

<=> 5×b + 40 = 0

<=> 5b = -40

=> b = -8

Replace b with -8 in (1), we have the equation:

2x^2 − 8x − 10=0

<=> 2(x^2 − 4x − 5) = 0

<=> 2(x^2 + x - 5x − 5) = 0

<=> 2[x(x + 1) - 5(x + 1)] = 0

<=> 2(x + 1)(x - 5) = 0

=> x = -1, or x = 5