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7)25x^2 + 9x = 0
8)-x^2 + 2x = 0
9)16x^2 - 9 = 0

7) 25x^2 + 9x = 0

25x^2 + 9x + 0 = 0

D = 9^2 - 4*25*0 = 9^2

x1 = (-9 - 9)/(2*25) = -18/50 = -9/25

x2 = (-9 + 9)/(2*25) = 0/50 = 0

8) -x^2 + 2x = 0

-x^2 + 2x + 0 = 0

D = 2^2 - 4(-1)*0 = 2^2

x1 = (-2 - 2)/(2(-1)) = -4/(-2) = 2

x2 = (-2 + 2)/(2(-1)) = 0/(-2) = 0

9) 16x^2 - 9 = 0

16x^2 + 0x - 9 = 0

D = 0^2 - 4*16(-9) = 64*9 = 576 = 24^2

x1 = (0 - 24)/(2*16) = -24/32 = -3/4

x2 = (0 + 24)/(2*16) = 24/32 = 3/4

7)

8)

9)

Ответ: 7) -9/25 и 0

           8) 0 и 2

           9) -0.75 и 0.75