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solve this equation using the quadratic formula; 2x^2 + x = 15

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2 Answers

2x2 + x = 15
2x2 + x - 15 = 0
(2x - 5) (x + 3) = 0
 
If the product of the two expressions is zero, then one or both of the factors must be zero. Find those values of x that make each factor equal to zero:
 
2x -5 = 0
2x = 5
x = 5/2
 
x + 3 = 0
x = -3
 
x = -3, and x = 5/2
 
ax^2 + bx + c = 0
D = b^2 - 4ac
x12 = (- b ± √D) / 2a


2x^2 + x - 15 = 0

a = 2, b = 1, c = - 15

D = 1 + 120 = 121

x12 = (- 1 ± √121) / 4

x1 = (- 1 + 11) / 4 = 5/2 = 2.5 

x2 = (- 1 - 11) / 4 = - 3