Найдите значение (7*-8) (7*+8) - 7 * (7*+8) при * = 3,5

(7 х-8) (7 х+8) - 7 х (7 х+8) = - 81,25.

(7•3,5-8) (7•3,5+8) - 7•3,5 (7•3,5+8) = - 81,25.

1) 7•3,5=24,5;

2) 24,5-8=16,5;

3) 7•3,5=24,5;

4) 24,5+8=32,5;

5) 7•3,5=24,5;

6) 24,5+8=32,5;

7) 24,5•16,5=404,25;

8) 3,5•32,5=113,75;

9) 113,75•7=950,25;

10) 32,5-113,75 = - 81,25.

Ответ: - 81,25.

(7x - 8) (7x + 8) - 7x (7x+8) =

вынесем общий множитель:

= (7x+8) (7x - 8 - 7x) =

= (7x+8) * (-8) =

= - 56x - 64

= - (56 х + 64)

х = 3,5

- (56 * 3,5 + 64) = - (196 + 54) = - 250