Which of the following is not true?
A
$$7+8\times 9=(7+8)\times (7+9)$$
B
$$7\times (8+9)=(7\times 8)+(7\times 9)$$
D
$$(7\times 8)\times 9=7\times (8\times 9)$$
Correct option is C. $$7+8\times 9=(7+8)\times (7+9)$$
$$\textbf{Step 1: Recall Associative property of addition and multiplication.}$$
By Associative property of addition and multiplication we have
$$(7 + 8) + 9 = 7 + (8 + 9) $$ and $$(7 \times 8) \times 9 = 7 \times (8 \times 9)$$ are correct
$$\therefore\ \textbf{Option A and B are true}$$.
$$\textbf{Step 2: Recall Distributive property of multiplication over addition}$$
By distributive property of multiplication over addition we have
$$7 \times (8 + 9) = (7 \times 8) + (7 \times 9)$$ is correct.
$$\textbf{So Option D is also true}$$.
$$7 + 8 \times 9 = 7 + 72$$
$$ = 79$$
$$(7 + 8) \times (7 + 9) = 15 \times 17$$
$$= 255$$
So $$7 + 8 \times 9 = (7 + 8) \times (7 + 9)$$ is incorrect.
$$\therefore\ \textbf{Option C is not true}$$.
$$\textbf{Therefore the correct option is C}$$.