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518.
х+2у=-2 -у=8-3х
3х-у=8 у=3х-8
х+2*(3х-8)=-2
х+6х-16+2=0
7х-14=0
7х=14 х=14/7 х=2
519.
х-у=3 х=3+у
3х+4у=2 3*(3+у)+4у-2=0
9+3у+4у-2=0
7+7у=0
7у=-7 у=-7/7 у=-1
520.
2х+3у=-7 х=4+у
х-у=4 2*(4+у)+3у+7=0
8+2у+3у+7=0
15+5у=0
5у=-15 у=-15/5 у=-3
Sina=0,8 90<a<180
cosa=(+-)√(1-sin²a)=(+-)√1-0,8²)=(+-)√1-0,64)=(+-)√0,36=(+-)0,6
90<a<180 => a∈ II четверти => cosa<0
cosa=-0,6
16-88у+121у²-1=0
121у²-88у+15=0
у₁=<u>88+√(7744-7260)</u> = <u>88+22</u> = <u>110</u> = 5/11
242 242 242
у₂=<u>88-√(7744-7260)</u> = <u>88-22</u> = <u>66</u> = 3/11
242 242 242
16t²-24t+9-25t²=0
-9t²-24t+9=0
3t²+8t-3=0
t₁=<u>-8+√(64+36)</u> = <u>-8+10</u> = 1/3
6 6
t₂=<u>-8-√(64+36)</u> = <u>-8-10</u> = -3
6 6
2) x^3 ( y^3 - 2 ) + 5 ( y^3 - 2 ) = (y^3 - 2) (x^3 + 5)
4) 9 ( 3 - x^2 ) + y^6 ( 3 - x^2 ) = (3 - x^2 ) ( 9 +y^6)