How does $ a^{2^i}a^{2^i} $ become $ a^{2^{i+1}} $?

Question

I have this expression: $$ a^{2^i}a^{2^i} $$

My slides convert this into: $$ a^{2^{i+1}} $$

I however don't see how to convert $$a^{2^{i}+2^{i}}$$ into that resultant form.

Which math rule am I missing here?

Answer 1

$a^{2^i}\cdot a^{2^i}=a^{2^i+2^i}=a^{2\cdot 2^i}=a^{2^{i+1}}$