Question

помогите пожалуйста всё 4 5 6​

Answer 1

Ответ:

4

$(7x+1)(x-3)+20(x-1)(x+1) = 3(3x-2)^{2} +13\\7x^{2} -21x+x-3 + 20(x^{2}-1) = 3(9x^{2} -12x+4)+13\\ 7x^{2} -20x-3 + 20x^{2} -20 = 27x^{2} -36x+12+13\\27x^{2} -20x-23 = 27x^{2} -36x+25\\16x=48\\x=3$

5)

$(2a+1)^{2} - (a-9)^{2} = (2a+1+a-9)*(2a+1-a+9) = (3a-8)*(a+10)$

6)

$(b-5)(b+5)(b^{2} +25) - (b^{2} -9)^{2} = \\=(b^{2} -25)(b^{2}+25) - (b^{2} -9)^{2}= \\ = b^{4} - 625 - (b^{4} -18b^{2} +81) = \\ = b^{4} - 625 - b^{4} +18b^{2} -81 = \\ = 18b^{2} -706 = 2(9b^{2} - 353)$

b= -1/3

2(9*$\frac{1}{9}$-353) = 2(1-353) = 2*-352 = -704