Question 483870
Boat speed		x   		
current speed 		3		
				
against current x-		3	kph	
with current x+		3	kph	
				
Distance= 	54	km		
				
Time against + time with  = 			5.25	hours
t=d/r				
54	/(	x   	+	3	)	+	54	/(x	-	3	)	=	5.25				
																	
LCD =	(x	-	3	)	(	x   	+	3	)								
54	*(	x   	-	3	)	+	54	(x	+	3	)	=	5.25				
54	x   	-	162	+	54	x   	+	162		=	5.25	(	x ^2		-	9	)
108	x   	=	5.25	x ^2	-	47.25											
5.25	x ^2	-	-108	x   	-	47.25											
																	
Find the roots of the equation by quadratic formula			
a=	5.25	,	b=	-108	,	c=	-47.25										
																	
b^2-4ac=11664	+	992.25														
b^2-4ac=12656.25
{{{	sqrt(	12656.25	)=	112.5	}}}									
{{{x=(-b+-sqrt(b^2-4ac))/(2a)}}}																	
{{{x1=(-b+sqrt(b^2-4ac))/(2a)}}}																	
x1=(	108	+	112.5	)/	10.5												
x1=	21																
x2=(	108	-112.5	) /	10.5													
x2= 	-0.43																
Ignore negative value	
boat speed = 21 kph