4x^2-5x-7=0

3x^2+2x=0

x^4-17x^2+16=0

найти дескрименант

4 х² - 5 х - 7 = 0

D = b² - 4ac = 25 - 4·4· (-7) = 25 + 98 = 123

3 х² - 17 х + 16 = 0

D = b² - 4ac = 289 - 4·3·16 = 289 - 192=97

x^4 - 17x^2 + 16 = 0

x^2 = t

t^2 - 17t + 16 = 0

по т. Виета t1 = 1 и b2 = 16

x^2 = 1 x^2 = 16

x = + - 1 x = + - 4