First, bring the equation to the form ax²+bx+c=0 :
10x² + 23x - 42 = 0
Let's use quadratic formula: quadratic formula:
x =( -b ± √(b² - 4a*c) )/2a
a = 10
b=23
c=-42
x = (-23 ± √((-23)² - 4*10*-42)/2*10
x = (-23 ± √2209)/20
x1 = (-23 + √2209)/20 = (-23+47)/20 = 6/5 = 1.2
x2 = (-23 - √2209)/20 = (-23-47)/20 = -7/2 = -3.5