Find b and then solve the equation

Question

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

2x²+bx−10=0, if one of its roots is 5

Answer 1

2(5^2) + 5B - 10 = 0

 

2(25) + 5B - 10 = 0

 

50 + 5B - 10 = 0

 

5B + 40 = 0

 

b = -40/5 = -8

 

So the original quadratic equation is 2x^2 - 8x - 10 = 0

 

  Factoring out and dividing by 2:   x^2 - 4x - 5 = 0

 

                                                (  x     -    5 )( x   +      1  ) = 0

 

   x- 5 = 0 ---> x = 5 which was given

 

  x+1 = 0   --> x= -1.

 

CHECK STEP:

   2*(-1)^2 - 8(-1) - 10 = 2(1) - 8(-1) - 10 = 2 + 8 - 10 = 10 - 10 = 0