Simplify (2d^7)(-4d^9d^5)

$(2 d^{7}) (- 4 d^{9} d^{5})$

Multiply $d^{7}$ by $d^{9}$ by adding the exponents.

Move $d^{9}$ .

$2 (d^{9} d^{7}) (- 4 d^{5})$

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$2 d^{9 + 7} (- 4 d^{5})$

Add $9$ and $7$ .

$2 d^{16} (- 4 d^{5})$

Rewrite using the commutative property of multiplication.

$2 \cdot - 4 d^{16} d^{5}$

Multiply $d^{16}$ by $d^{5}$ by adding the exponents.

Move $d^{5}$ .

$2 \cdot - 4 (d^{5} d^{16})$

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$2 \cdot - 4 d^{5 + 16}$

Add $5$ and $16$ .

$2 \cdot - 4 d^{21}$

Multiply $2$ by $- 4$ .

$- 8 d^{21}$