<p>For example: For all positive integers x, let x▲ be defined to be (x-1)(x+1). Which of the following is equal to 6▲-5▲?</p>
<p>I found the answer online, and I know how the problem should be approached and solved, but what does that ▲ (triangle) mean? I think I read somewhere in a review book that ETS likes to use symbols, like ▲, to substitute for f(x)=, but I can't be sure.</p>
<p>Thanks.</p>
<p>It’s exactly like f(x) but instead they use symbols. </p>
<p>Just plug in the number next to the triangle. </p>
<p>Ex: 6▲-5▲ = (6-1)(6+1) - (5-1)(5+1)</p>
<p>It is just a fake mathematical operator, and the problem is merely a simple plug and chug. They use those problems to fluster you (OMG, I never learned triangles!! ■■■!!).</p>
<p>It’s to confuse people who don’t know the definition of a function.</p>