Which quadratic equation is equivalent to open paren x plus 2 close paren squared plus 5 times open paren x plus 2 close paren minus 6 is equal to 0 ?

Let u = x + 2, which matches the repeated expression in the original equation. Then (x + 2)² becomes u² and 5(x + 2) becomes 5u, so the equation is u² + 5u − 6 = 0. This is choice D.

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