2)= -9с²+9с²+d²-d²=0
4)= (7b-t)(7b+t)+49b²+t²=49b²-t²+49b²+t²=98b²
6) =121c²+9-(11c²+66c)=121c²+9-11c²-66c=110c²+9-66c
P = 2(a + b) = 10
S = a*b = 6
a + b = 5
a*b = 6
a = 5 - b
b(5 - b) - 6 = 0 *
* - b^2 + 5b - 6 = 0
b^2 - 5b + 6 = 0
D = 25 - 24 = 1
b1 = ( 5 + 1)/2 = 6 /2 = 3;
b2 = ( 5 - 1)/2 = 4/2 = 2;
a1 = 5 - b1 = 5 - 3 = 2
b1 = 3
a2 = 5 - b2 = 5 - 2 = 3
b2 = 2
Ответ:
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1)60÷х=20
х=60÷20
х=3
3 ч туда,и 3 часа обратно
2)3+3=6ч
3)6ч25 мин-6ч=25 мин.
4)60÷25=1,15км/ч