Sub in given values to get 2 equations.
![a + b \cos(2*0) = -1 \rightarrow a+b = -1 \\ \\ a+b \cos(2*\frac{\pi}{2}) = 7 \rightarrow a - b = 7](https://tex.z-dn.net/?f=a%20%2B%20b%20%5Ccos%282%2A0%29%20%3D%20-1%20%5Crightarrow%20a%2Bb%20%3D%20-1%20%5C%5C%20%20%5C%5C%20a%2Bb%20%5Ccos%282%2A%5Cfrac%7B%5Cpi%7D%7B2%7D%29%20%3D%207%20%5Crightarrow%20a%20-%20b%20%3D%207)
Solve system using elimination. Add the equations together, cancelling out 'b'
![2a = 6 \\ \\ a = 3](https://tex.z-dn.net/?f=2a%20%3D%206%20%5C%5C%20%20%5C%5C%20a%20%3D%203)
Sub into first equation to get value for 'b'
1. no because 2x+10 is not equal to 2x+7
2. no. you cant add una like terms so 4x+4 doesn’t equal 8x
3. yes. the terms still retain their same value although they are not in the same order
4. yes. when u distribute the -3, you get -3x-6 which is of course equal to -3x-6
8. is 16
10. is 5
11. is 10