Your example is not an equation (it's an identity). An equation contains one or more unknowns. For example 12x - 4 = 8 is a linear equation in a single unknown. You add or subtract terms to both sides so that similar types are together. In the above you would add 4 to both sides to get the constants together: 12x - 4 + 4 = 8 + 4 or 12x = 12. Now you divide both sides by 12 to isolate the unknown: 12x/12 = 12/12 or x = 1. Now you have solved for what was originally unknown.
Has this helped?
x*y = 10 so y = 10/x
x + y = 9, so x + 10/x = 9 Multiply through by x and rearrange to get x^2 - 9x +10 = 0 Solve using the quadratic equation.
343 = 7^3, so log7 343 = log7 7^3 = 3 log7 7 = 3
Hmm!
Like this:
I'll leave you to finish it.
\(2z+i = iz+3\\ z(2-i)=3-i\\z=\frac{3-i}{2-i}\\z=\frac{3-i}{2-i}\times\frac{2+i}{2+i}\\z=\frac{(3-i)(2+i)}{2^2-i^2}\)
Can you take it from here?
Yes, except you should put cos(2*11) rather than cos2(11).
Note that cos(22) = √(1 - k^2) from the previous result.
Also cos(22) = cos(11 + 11) = 1 - 2*sin(11)^2
Can you take it from there?
cos(158) = cos(180 - 22) = cos(180)*cos(22) + sin(180)*sin(22) = -cos(22) = -√(1-sin(22)^2) = - √(1 - k^2)
+33666 
