Question

помогите срочно нужнл​

Answer 1

Объяснение:

1)

(5+b)(b-5)-b² = (b+5)(b-5)-b²=

= (b²-5²)-b²= -5²= -25

2)

c²+(9-c)(9+c) = c² + 9²-ç² =

= -9² = -81

3)

$( \frac{1}{3} - z)( \frac{1}{3} + z) - \frac{1}{9} = \\ ( \frac{1}{3}) {}^{2} - {z} {}^{2} - ({ \frac{1}{3} })^{2} = - z {}^{2}$

4)

$- \frac{16}{49} + ( \frac{4}{7} - d)(d + \frac{4}{7} ) = - \frac{16}{49} + ( \frac{4}{7} - d)( \frac{4}{7} + d) = \\ = - \frac{16}{49} + ( \frac{4}{7} ) {}^{2} - d {}^{2} = - \frac{16}{49} + \frac{16}{49} - d {}^{2} = - {d}^{2}$

5)

(0.9-a)(a+0.9)-a(1+a) =

0,9² - a² - (a + a²) = 0,81-a-a²

6)

k (5-k)+(1,2+k)(k-1,2)=

= (5k-k²)+(k+1,2)(k-1,2)=

5k - k² + k² - 1,2² = 5k - 1,2² =

= 5k - 1,44