Question 771459
A(-3,-2) B(5,2) C(9,4)

you have to calculate the three distances
and then prove

l(AB)
Distance between two points													
x1	y1	x2	y2										
													
-3	-2	5	2										
d=	{{{sqrt((y2-y1)^2+(x2-x1)^2)}}}												
d=	{{{sqrt((		2	-	-2	)^2	+	(	5	-	-3	)^2	)}}}
d=	{{{sqrt((		4	)^2	+	(	8	)^2	)}}}				
d=	{{{sqrt((		80	)  	)}}}								
d=	8.94		

l(BC)		

Distance between two points													
x1	y1	x2	y2										
													
9	4	5	2										
d=	{{{sqrt((y2-y1)^2+(x2-x1)^2)}}}												
d=	{{{sqrt((		2	-	4	)^2	+	(	5	-	9	)^2	)}}}
d=	{{{sqrt((		-2	)^2	+	(	-4	)^2	)}}}				
d=	{{{sqrt((		20	)  	)}}}								
d=	4.47												
l(AC)

Distance between two points													
x1	y1	x2	y2										
													
9	4	-3	-2										
d=	{{{sqrt((y2-y1)^2+(x2-x1)^2)}}}												
d=	{{{sqrt((		-2	-	4	)^2	+	(	-3	-	9	)^2	)}}}
d=	{{{sqrt((		-6	)^2	+	(	-12	)^2	)}}}				
d=	{{{sqrt((		180	)  	)}}}								
d=	13.42											

4.47 +8.94 = 13.42	
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