The value of (21)² - (19)² = ____?
- 40
- 60
- 80
- None of these
Explanation
We can use the formula for the difference of squares:
a² - b² = (a - b)(a + b)
Here a = 21, b = 19
21² - 19² = (21 - 19)(21 + 19)
= (2)(40) = 80
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