Alan

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?

Like this:

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)