3) x² - 121 = 0
x² = 121
x' = +√121
x' = 11
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x'' = - √121
x'' = -11
Solution ⇒ S{-11 ; 11 } or (x-11)(x+11)
4) 4x² + 144 = 0
4x² = -144
x² = -144 / 4
x² = -36
x = √-36
No solution ⇒ S = ∅
5) z²+10z+21 = 0
Δ = 10² - 4(1)(21)
Δ = 100 - 84
Δ = 16
x' = (-10+4) / 2 = -6/2 = -3
x'' = (-10-4) / 2 = -14/2 = -7
Solution ⇒ S{ -7 ; -3} or (x+3)(x+7)
If you divide 13 by 3 you get 4 1/3 then you subtract 25 by 4 1/3 to get 20 2/3 so the answer is B
X=-15 because you have to add 3 on both sides
