Doubt in Euler's proof Basel problem

Question

In the proof of the Basel problem Euler reaches a step where expansion of $(\sin x)/x$ is $[1-(x^2/\pi^2)][1-(x^2/4\pi^2)][1-(x^2/9\pi^2)]\cdots$ And from that he got to- $1- x^2\{1/\pi^2 + (1/4\pi^2) + (1/9\pi^2) +\cdots\}+ x^4(\cdots)+\cdots$. I don't understand how this happens?