jika f(x)=2x + 5 dan g(x)=x² dan f(x)=g(x) maka nilai x adalah?

Bab Fungsi
Matematika SMP Kelas VIII

f(x) = g(x)
2x + 5 = x²
x² - 2x - 5 = 0
a = 1; b = -2; c = -5

x12 = (-b +- √(b² - 4ac))/(2 x a)
       = (-(-2) +- √((-2)² - 4 x 1 x (-5)) / (2 x 1)
       = (2 +- √(4 + 20))/2
       = (2 +- √24)/2
       = (2 +- 2√6)/2

x1 = 1 + √6
x2 = 1 - √6