2*(5-y)-9y=21 — step-by-step solution

Let's solve in

ℝ

2 \cdot (5 - y) - 9 y = 21

ⓘ Expand by multiplying each term inside the parentheses:

2 \cdot (5 - y)

10 + 2 \cdot (- y)

10 + 2 \cdot (- y) - 9 y = 21

ⓘ The minus sign is placed in front of the product:

2 \cdot (- y)

- 2 y

10 - 2 y - 9 y = 21

ⓘ Like terms are grouped by adding their coefficients:

- 2 y - 9 y

-11 y

10 - 11 y = 21

ⓘ We gather the terms in

y

on the right and the other terms on the left

10 - 21 = 11 y

ⓘ Start from

10

and move back

21

on the number line, going below zero:

10 - 21

-11

-11 = 11 y

ⓘ Both sides are divided by

11

y = - \frac{11}{11}

ⓘ We simplify the fraction by dividing the numerator and the denominator by

11

, their greatest common divisor:

- \frac{11}{11}

-1

▶Solution found:

y = -1