4 ms·
No need to memorize (10a+5)² = [a * (a+1)][25] (a+1)² = a² + a + (a+1) (a-1)² = a² - a - (a-1) (a+2)² = a² + 4(a+1) (a-2)² = a² - 4(a-1)
by lupire 2y ago
No need to memorize
(10a+5)² = [a * (a+1)][25]
(a+1)² = a² + a + (a+1)
(a-1)² = a² - a - (a-1)
(a+2)² = a² + 4(a+1)
(a-2)² = a² - 4(a-1)