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Sin x = 0,21; cos x = √(1 - sin^2 x) = √(1 - 0,0441) = √(0,9559)
![sin(x/2)= \sqrt{ \frac{1-cos(x)}{2} } = \sqrt{ \frac{1- \sqrt{0,9559} }{2} }](https://tex.z-dn.net/?f=sin%28x%2F2%29%3D+%5Csqrt%7B+%5Cfrac%7B1-cos%28x%29%7D%7B2%7D+%7D+%3D+%5Csqrt%7B+%5Cfrac%7B1-+%5Csqrt%7B0%2C9559%7D+%7D%7B2%7D+%7D+)
![cos(x/2)= \sqrt{ \frac{1+cos(x)}{2} } = \sqrt{ \frac{1+ \sqrt{0,9559} }{2} }](https://tex.z-dn.net/?f=cos%28x%2F2%29%3D+%5Csqrt%7B+%5Cfrac%7B1%2Bcos%28x%29%7D%7B2%7D+%7D+%3D+%5Csqrt%7B+%5Cfrac%7B1%2B+%5Csqrt%7B0%2C9559%7D+%7D%7B2%7D+%7D+)
![sin(x/2)+cos(x/2)=\sqrt{ \frac{1- \sqrt{0,9559} }{2} }+\sqrt{ \frac{1+ \sqrt{0,9559} }{2} }](https://tex.z-dn.net/?f=sin%28x%2F2%29%2Bcos%28x%2F2%29%3D%5Csqrt%7B+%5Cfrac%7B1-+%5Csqrt%7B0%2C9559%7D+%7D%7B2%7D+%7D%2B%5Csqrt%7B+%5Cfrac%7B1%2B+%5Csqrt%7B0%2C9559%7D+%7D%7B2%7D+%7D)
≈ 0,1056 + 0,9944 = 1,1
3х-5bу+5b-a=18 вмсто х и у в уравнение подставит х=-1 иу=2 также и во 2-м уравнении тогда получим,
3(-1)-5b2+5b-a=18
-3-10b+5b -a=18
-3-5b-a=18
-5b-a=21
-5(-5)-4=21
значит а=-5,b=4
ax+7y+3a=12
-1a+7*2+3a=12
-a+14+3a=12
2a=-2
a=-1,b=0