-5x^2-7x-13=0 эквивалентно 5x^2+7x+13=0
D=49-4*5*13<0 решений нет
7х-8у=3 |х-3
21х+2у=113
-21х+24у=-9
21х+2у=113
26у=104
у=4
7х-8·4=3
7х=3+32
х=5
9 × а^8 × b^14 / (-3 × a^3 × b^4)^3 =
9 × а^8 × b^14 / -9 × a^9 × b^12 =
-1 × (a^-1 × b^2) =
-1 × (1/a × b^2) =
-1 × (b^2/a) =
-b^2/a