CPM Homework Help : INT3 Problem 12-5

Decide if each of the following equations is always true, sometimes true, or never true. If an equation is always true, justify how you know; if it is sometimes true, give the exact values of $x$ that make it true; and if it is never true, explain why it is never true.

$3x - 2 - 4\left(x + 1\right) = -x - 6$
Hint (a):
Simplify the part of the equation on the left side of the equals sign.
Does it equal the part on the right side?
Answer (a):
Always.

$3x - 5 = 2\left(x + 1\right) + x$
Hint (b):
Use the same method as part (a).

$\sin(x)=\cos(\frac{\pi}{2}-x)$
Hint (c):
Substitute values into the equations for $x$ .
Are they always equal?
Answer (c):
Always.

$\tan(x)=1$
Hint (d):
Is this always true?
If not, what values of $x$ would make it true?