7х - 4 = х - 16
7х - х = - 16 + 4
6х = - 12
х = - 2
<u>проверка:</u>
7 * (- 2) - 4 = - 2 - 16
-14 - 4 = -2 - 16
- 18 = - 18
-x^2+8x-9=0
D=64+36=100
x1=(-8+10)\-2=-1
x2=(-8-10)\-2=9
159²-159×118+59²=25281-18762+3481=10000=
=10⁴
1/30+2/9=3/90+20/90=23/90