Question

Find the value of 399^2

- 398^2​

Answer 1

Answer:

$399 {}^{2} - 398 {}^{2} \\ (400 - 1) {}^{2} - (400 - 2) {}^{2} \\ 1600 -800 + 1 - 1600 + 1600 - 4 \\ 1600 + 1 - 800 - 4 \\ 800 - 3 \\ 797$

another method is (a^2-b^2) = (a+b)(a-b)

Answer 2

399² - 398² = 797

Given :

The expression 399² - 398²

To find :

The value of the expression

Formula :

a² - b² = ( a + b ) ( a - b )

Solution :

Step 1 of 2 :

Write down the given expression

The given expression is 399² - 398²

Step 2 of 2 :

Find the value of the expression

Use the formula a² - b² = ( a + b ) ( a - b )

$\sf {399}^{2} - {398}^{2}$

$\sf = (399 + 398) \times (399 - 398)$

$\sf =797 \times 1$

$\sf = 797$

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