Explanation:
again, we can transform every equation by doing the same operations on both sides of the "=" sign.
really every operation and function is possible normally, as long as you apply them to both sides.
1.
P = 2(l + b) = 2l + 2b
now to have only b on one side. what do we need to do ?
first, let's move 2l to the other side. we do this by subtracting 2l from both sides :
P - 2l = 2b
ok, and now, how do we get b from 2b ? by dividing by 2 ! again, as always, in both sides :
(P - 2l)/2 = b
b = (161 - 2×45)/2 = (161 - 90)/2 = 71/2 = 35.5 cm
2.
C = 2×pi×r
r should be alone on one side. what do we do ?
let's first divide by 2 (on both sides) :
C/2 = pi×r
ok, and now the same trick just with pi. we divide both sides by pi :
C/(2pi) = r
r = 144.44/(2×3.14) = 144.44/6.28 = 23 cm
3.
m = 5t²
now, we want to get t all by itself on one side.
first we divide (both sides) by 5 :
m/5 = t²
and how do we get t from t² ? by pulling the square root (sqrt()). again, as always, on both sides :
t = sqrt(m/5)
t = sqrt(180/5) = sqrt(36) = 6 seconds