Question

Let the expression m Δ n be defined to mean 2mn + m. Then 3(5 Δ 7) =
A) 75
B) 105
C) 210
D) 225
E) 280

Answer 1

let's dissect what this means

"m Δ n be defined to mean 2mn + m"

so this tells you that, when you have any expression with a number (m) in front of a triangle, then a triangle, then a second number (n) after the triangle, the expression is equal to

2mn +m

(2, multiplied by the first number, multiplied by the second number, then added to the first number again)

now, can you try applying this to 5 Δ 7 first?

Answer 2

yea