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

find x and b

x = - 1, or x = 5

b = - 8

Step-by-step 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