Algebra 1

Use the Pythagorean Theorem to find the missing length. $a^2+b^2=c^2\longrightarrow$ substitute the given values $a^2+36^2=39^2\longrightarrow$ simplify exponents $a^2+1296=1521\longrightarrow$ subtract 1296 from each side $a^2+1296-1296=1521-1296\longrightarrow$ subtract $a^2=225\longrightarrow$ find the square root of each side $\sqrt{a^2}=\sqrt{225}\longrightarrow$ simplify $a=15$