An easy way to remember how to expand double brackets is using FOIL. FOIL stands for First, Outer, Inner, and Last. First indicates that we multiple the first two terms of each bracket (x * x = x²). Outer multiples the outer terms ( x * -3 = -3x). Inner multiplies the inner terms (5 * x = 5x). Finally, Last multiplies the last terms of each bracket (5 * -3 = -15). Our answer is the sum of the individual FOIL results: x² + (-3x) + 5x + (-15) = x² + 2x - 15.

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