Question 600811
Boat  	speed	x   	mph													
current     	speed	4	mph													
																
against	current     	x-	4	mph												
with	current     	x+	4	mph												
																
Distance=	8	miles														
																
Time against + time with  =2	hours												
t=d/r																
																
8/(x+4)	+8/(x-4)=	2			
																
LCD =(x-4)(x+4)							
8*(x-4)	+8(x+4)	=2(x^2-16)
8x-32+8x+32=2(x ^2-16)
16	x   	=	2	x ^2		-32										
2	x ^2	-	-16	x   	-	32	=0
divide by 2
x^2-8x-16=0									
																
Find the roots of the equation by quadratic formula																
																
a=	1	,	b=	-8	,	c=	-16									
																
b^2-4ac=	64	+	64													
b^2-4ac=	128															
{{{	sqrt(	128	)=	11.31	}}}											
{{{x=(-b+-sqrt(b^2-4ac))/(2a)}}}							
{{{x1=(-b+sqrt(b^2-4ac))/(2a)}}}																
x1=(	8	+	11.31	)/	2											
x1=	9.66															
{{{x2=(-b-sqrt(b^2-4ac))/(2a)}}}																
x2=(	8	-11.31	) /	2												
x2=	-1.66															
Ignore negative value																
Boat  	speed	9.66	mph													
																
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