x^2 + 5x - 10 = 0 can be re-written as x^2 + 5x + (5/2)^2 - (5/2)^2 = 0.
Then, x^2 + 5x + 25/4 = 10 + 25/4 = (40+25) / 4
(x+5/2)^2 = 65/4, so x+5/2 = plus or minus sqrt(65/4) = plus or minus 4.031.
Then x = -2.5 plus or minus 4.031, or x = -2.5+4.031 = 1.53 and
x = - 2.5 - 4.031 = -6.53 (answers)