Solve for s7 s_7=(3(1-2^7))/(1-2)

$s_{7} = \frac{3 (1 - 2^{7})}{1 - 2}$

Simplify the numerator.

Raise $2$ to the power of $7$ .

$s_{7} = \frac{3 (1 - 1 \cdot 128)}{1 - 2}$

Multiply $- 1$ by $128$ .

$s_{7} = \frac{3 (1 - 128)}{1 - 2}$

Subtract $128$ from $1$ .

$s_{7} = \frac{3 \cdot - 127}{1 - 2}$

$s_{7} = \frac{3 \cdot - 127}{1 - 2}$

Simplify the expression.

Subtract $2$ from $1$ .

$s_{7} = \frac{3 \cdot - 127}{- 1}$

Multiply $3$ by $- 127$ .

$s_{7} = \frac{- 381}{- 1}$

Divide $- 381$ by $- 1$ .

$s_{7} = 381$

$s_{7} = 381$

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