(20,6-2,4)*2=36,4 км проплывает против течения за 2 ч
( ab / c ) + d = xb - c
( ab + dc ) / c = xb - c
xb = ( ( ab + dc ) / c ) + c
xb = ( ab + dc + c^2 ) / c
x = ( ( ab + dc + c^2 ) / c ) : b
x = ( ab + dc + c^2 ) / bc
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ab + d = b( x - c )
x - c = ( ab + d ) / b
x = ( ( ab + d ) / b ) + c
x = ( ab + d + cb ) / b
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a + d = d( x + c )
x + c = ( a + d ) / d
x = ( ( a + d ) / d ) - c
x = ( a + d - cd ) / d
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ab / c = xd / c
ab = xd
x = ab / d
1)π/6
2)π
3)-π/4-π/2=-3π/4
4)х=-π/3+πn
5)2x=2πn⇒x=πn
6)x+π/4=(-1)^n*π/4+πn
x=-π/4+(-1)^n*π/4+πn=(-1)^n+1*π/4+πn