1)
(2а-11)(11+2а)-(2а-5)² = 0
(2а-11)(2а+11)-(2а-5)²=0
(2а)² - 11² - [(2а)²- 2·2a·5 + 5²] = 0
4a² - 121 - (4a² - 20a + 25) = 0
4a² - 121 - 4a² + 20a - 25 = 0
20a - 146 = 0
20a = 146
a = 146 : 20
a = 7,3
2)
(3х-8у)² = (3x)² - 2·3x·8y + (8y)² = 9x² - 48xy + 64y²
3)
(3,5t-4k)² = (3,5t)² - 2·3,5t·4k + (4k)² = 12,25t² - 28kt + 16k²