The possible numbers that Melody could have picked are -4 and 4.
The operation that prevents us from knowing with 100% certainty the number Melody had picked is multiplication which is implied by the phrase "double the number".
Given, Let x be the number Melody had chosen.
Thus, tripling the number will give 3x, and
squaring this will result to (3x)² which is equals to 9x².
Dividing the square of the number by 2 and subtracting 30 from its quotient will give 42:
9x²/2 ₋ 30 = 42
9x²/2 = 42 ₊ 30
9x²/2 = 72
9x² = 72 × 2
9x² = 144
x² = 144/9
x² = 16
x = ±√16
x = ±4
x = ₊4 or x = 4
hence melody could have picked ₊4 or ₋4 numbers.
Learn more about Equations here:
brainly.com/question/22688504
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