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А) 3x2-10x+3=0.
Б) 71x2+144x+4=0.
В) 9x2-30x+25=0.

3x²-10x+3= 0;D = 100 - 4 * 3 * 3 = 100 - 36 = 64x1 =( 10 - 8)/6 = 2/6 = 1/3x2 = (10+8)/6 = 3;71x² + 144x + 4 = 0;D = 20736 - 4 * 71 * 4 = 20736 - 1136 = 19600x1= (-144-140)/142 = -2;x2= (-144+140)/142 = -4/142 9x²-30x+25= 0;D = 900 - 4 * 9 * 25 = 0;x1 = 30/18 = 5/3