Question

solve this questions using the formula-
$(a + b)(a - b) = a{2} - b {2}$
1. 78×82
2. 10.5×9.5

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pls help me......☺☺

Answer 1

Hello friend,
Here's your required answer (©):

As (a + b)(a - b) = a² - b²

Q1. 78 × 82
=> (80 - 2)(80 + 2)
=> (80 + 2)(80 - 2) 
=> 80² - 2²
=> 6400 - 4
=> 6396
Q2. 10.5 × 9.5
=> (10 + 0.5)(10 - 0.5)
=> 10² - (0.5)²
=> 100 - 0.25
=> 99.75

Hope my answer helps you.