Question

Дано функцию f(x)=x в квдрате-9x+20.Найдите значение x при которых: 1.f(x)=0 2.f(x)=20 3.f(x)=12 3.f(x)=30

Answer 1

1. x^{2} - 9x + 20 = 0

x1, 2 = ( 9 +- sqrt{81 - 80} ) / 2; x1 = 4; x2 = 5

 

2.   x^{2} - 9x = 0 ; x = 9

 

3.   x^{2} - 9x + 20 = 12

x^{2} - 9x + 6 = 0

x1, 2 =  ( 9 +- sqrt{81 - 24} ) / 2; x1 approx 0.73; x2 approx 8.27 

 

4.   x^{2} - 9x - 10 = 0

x1, 2 = ( 9 +- sqrt{81 + 40} ) / 2; x1 = 10; x2 = 5