a) (7x - a)(7x + a) + a² = (7x)² - a² + a² = 49x²
б) (t + s)² + (t - s)² - 2t² = t² + 2ts + s² + t² - 2ts + s² - 2t² =
= 2t² + 2s² - 2t² = 2s²
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a) (7x - a)(7x + a) + a² = (7x)² - a² + a² = 49x²
б) (t + s)² + (t - s)² - 2t² = t² + 2ts + s² + t² - 2ts + s² - 2t² =
= 2t² + 2s² - 2t² = 2s²