Y=9-2x
5x+2*(9-2x)=7
5x-4x+18=7
x=-11
y=9-2*(-11)=20
Решение
<span>sin²x/4-cos²x/4=1/2
- (cos</span>²x/4 - sin²x/4) = 1/2
cos<span>²x/4 - sin²x/4 = - 1/2
</span>cos[2*(x/4)] = - 1/2
cosx/2 = - 1/2
x/2 = +-arccos(-1/2) + 2πk, k ∈ Z
x/2 = +- [π - arccos(1/2)] + 2πk, k ∈ Z
x/2 = +- [π - π/3<span>)] + 2πk, k ∈ Z
</span>x/2 = +- [2π/3<span>)] + 2πk, k ∈ Z
</span>x = +- [4π/3<span>)] + 4πk, k ∈ Z</span>
1)cos 7230 градусов = cos 30 = корень из 2 /2
<span>2)sin 900 градусов = sin 180 = 0
следовательно </span>cos7230+sin900=cos 30+sin 180=
![\sqrt{2 /2}](https://tex.z-dn.net/?f=+%5Csqrt%7B2+%2F2%7D++)
+ 0 =<span>
![\sqrt{2 /2}](https://tex.z-dn.net/?f=+%5Csqrt%7B2+%2F2%7D+)
Как-то так вроде...
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