Step-by-step explanation:
1) -9 = 9 true/false
the answer is false because negative and positive quite unlike in terms.
2) -(-21) = -21
Using the symbols multiplication rule,
Where,
<h2>+ × + = +</h2><h2>- × - = +</h2><h2>- × + = -</h2><h2>+ × - = -</h2>Therefore, -(-21) = +21 = 21
⟼ 21 = -21