Решить! 1.6x=3 2.4x-2=8 3.2x+1+2(2-x)=x 4.3(2-x)-2(2x+1)=3

Question

Алгебра: Решить! 1.6x=3 2.4x-2=8 3.2x+1+2(2-x)=x 4.3(2-x)-2(2x+1)=3

lex9090 · Accepted Answer

1) 4/5x² - 45 = 0
4x² - 225 = 0
4x² = 225
(2x)² = 225
2x = 15
x = 7,5
2) -2x² + 5x + 1 = -x² + 4x + (3 - x²)
-2x² + 5x + x² - 4x + x² = 3 - 1
x = 2
3) -3x² + 7x + 45 = (x + 6)²
     -3x² + 7x + 45 = x² + 12x + 36
-3x² - x² + 7x - 12x + 45 - 36 = 0
-4x² - 5x +9 = 0
D = b² - 4ac = (-5)² - 4 * (-4)*9 = 25 + 144 = 169
  √D = √169 = 13
-b + √D 5 + 13 18 9
x1 = = = - = - --- = -2,25
2a 2*(-4) 8 4

-b - √D   5 - 13 8
x2 = = = = 1
2a 2*(-4) 8

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