log (x^2 + 10x + 31) = 1, maka nilai dari (x1 + x2)^2 - 3x1x2 adalah

jawab

log (x² +10x +31)= 2
x² +10x + 31 = 10² = 100
x² + 10x + 31 - 100 =0
x² + 10x - 69 = 0
akar akar x1 dan x2
x1 + x2 = -b/a = -10/a = -10
x1 x2 = c/a = -69/1 = -69

(x1 + x2)² - 3(x1 x2) = (-10)² - 3(-69)
= 100 + 207
= 307