To estimate a square root, find the two perfect squares the number is closest to, then continue with further decimals, i.e. if the question is square root of 5, it is between 4 and 9. As such, the answer is between 2 and 3. Alternatively, use a calculator for a quick estimation of many decimal points.
-20+1= -19
-19/2= -9.5
Check:
-9.5x2= -19
-19-1= -20
3r-6=-21
3r-6+6=-21+6 (Add 6 to both sides...)
3r=-15
r=-5
3r-6=21
3r-6+6=21+6 (Add 6 to both sides...)
3r=27
r=9
r=-5 or r=9
