Question 916873
boat   	speed	x   	mph		Time forward + time return = hours												
current     	speed	5	mph														
																	
against	current     	x-	5	km/h													
with	current     	x+	5	km/h													
																	
Distance=	10	miles															
																	
Time against + time with  =			3	hours													
t=d/r																	
																	
10	/(	x   	+	5	)	+	10	/(x	-	5	)	=	3				
																	
LCD =	(x	-	5	)	(	x   	+	5	)								
10	*(	x   	-	5	)	+	10	(x	+	5	)	=	3	(x^2	-	25	)
10	x   	-	-50	+	10	x   	+	50		=	3	(	x ^2		-	25	)
20	x   	=	3	x ^2		-75											
3	x ^2	-	-20	x   	-	-75	=	0									
																	
Find the roots of the equation by quadratic formula															5.12		
																	
a=	3	,	b=	-20	,	c=	-75										
																	
b^2-4ac=	400	+	900														
b^2-4ac=	1300																
{{{	sqrt(	1300	)=	36.06	}}}							379.94					
{{{x=(-b+-sqrt(b^2-4ac))/(2a)}}}																	0
{{{x1=(-b+sqrt(b^2-4ac))/(2a)}}}																	
x1=(	20	+	36.06	)/	6												
x1=	9.34																
{{{x2=(-b-sqrt(b^2-4ac))/(2a)}}}																	
x2=(	20	-36.06	) /	6													
x2=	-2.68																
Ignore negative value																	
boat   	speed	9.343	km/h														
																	
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