10) a = xy² + x²y, b = 3xy² - x²y
a + b = (xy² + x²y) + (3xy² - x²y) = xy² + x²y + 3xy² - x²y = 4xy²
a - b = (xy² + x²y) - (3xy² - x²y) = xy² + x²y - 3xy² + x²y = -2xy² + 2x²y
Ответ: a + b = 4xy², a - b = -2xy² + 2x²y