7х+у=20
у=20-7х
у=13
13+7х=20
20=20
Ответ:у=20
х-5у=8
х+5у=8
х=13
13-5у=8
8=8
Ответ:х=13
Вынесем 4x получим
4x(x-4)=0
x1=0 x2=4
<span>вроди-бы так
=синус 51-21=синус30= 1/2</span>
<span>1
(1+sin2h)/cos2h=tg(pi/4+h)</span><span>
(1+sin2h)/cos2h=(cosh</span>²+sin²h+2sinhcosh)/(cos²h-sin²h)=
=(cosh+sinh)²/(cosh-sinh)(cosh+sinh)=<span>(cosh+sinh)/(cosh-sinh)
tg(</span>π/4+h)=sin(π/4+h)cos(π/4+h)=(sinπ/4cosh+cosπ/4sinh)/(cosπ/4cosh-sinπ/4sinh)=√2/2(cosh+sinh)/√2/2(cosh-sinh)=<span>(cosh+sinh)/(cosh-sinh)
</span>(cosh+sinh)/(cosh-sinh)=<span>(cosh+sinh)/(cosh-sinh)</span>