Question 470745
first part	x	mph													
second part	-5	mph													
															
first part	90	miles													
second part	12	miles													
															
speed in first part	x			mph											
speed second part	x		-5	mph											
Total rowing time		5	hours												
Time first part		90	/	x											
Time second part		12	/	(	x	-5	)								
															
Time first part + time second part =			5	hours											
															
90/x+12/(x-5)=	5			
LCD =(x)*(x-5)							
multiply the equation by the LCD															
we get															
90*(x-5)+12x				=	5			
90x-450+	12x=5x^2-25x
127x-450	=5x^2										
5X^2-127	x+450=0							
5X^2-127	x+450	=0									
/5														
x^2-25.4	x+90=0									
															
Find the roots of the equation by quadratic formula			a=	1	b=	-25.4	c=	90										
															
b^2-4ac=	645.16-(	-360)												
b^2-4ac=	285.16	
{{{sqrt(	285.16)}}}=	16.89								
{{{x=(-b+-sqrt(b^2-4ac))/(2a)}}}															
{{{x1=(-b+sqrt(b^2-4ac))/(2a)}}}															
x1=(	25.4	+	16.89	)/	2										
x1=	21.14	====>	21 1/7												
x2=(	25.4	-16.89	) /	2											
x2= 	4.26	===>	4 1/4	(Ignore this  value)															
x	=	21.14	mph	LCD =speed 
first part 21.94 mph
seond part 21.14-5=16.14 mph								
m.ananth@hotmail.ca