58:(x+4)+42:(x-4)=100:x
58x(x-4)+42x(x+4)=100(x+4)(x-4)
58x²-232x+42x²+168x=100x²-1600
100x²-58x²-42x²+232x-168x-1600=0
64x-1600=0
64x=1600
x=1600:64=25 км/ч
<span>(3+√21)(√3-√7) =√3(√3+√7)(√3-√7)=√3(√3²-√7²)=√3(3-7)=-4√3</span>
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