Triangle Geometry

Geometry Level 2

As shown in the diagram above, A B = 8 \overline { AB } =8 and A C = 15 \overline { AC } =15 . Also B A C = 9 0 o \angle BAC=90^o and B C D = 9 0 o \angle BCD=90^o . If y = 53.1 o y={ 53.1 }^{ o } and D C = 4 \overline {DC} = 4 , what is the area (to the nearest unit) of the blue shaded triangles?

Diagram is not drawn to scale.


The answer is 70.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

1 solution

Stewart Feasby
Oct 10, 2014

Firstly, using Pythagoras' Theorem, we can say that: B C = 8 2 + 1 5 2 \overline {BC} = \sqrt {8^2 + 15^2} B C = 64 + 225 = 289 = 17 \overline {BC} = \sqrt {64 + 225} = \sqrt {289} = 17 Therefore: B C D = 17 × 4 2 = 68 2 = 34 \triangle BCD = \frac {17\times 4}{2} = \frac {68}{2} = \boxed {34} Now, using right-triangle trigonometry, we know that S i n ( θ ) = O H Sin(\theta)=\frac O H , therefore: s i n ( 53.1 ) = 8 H sin(53.1)=\frac 8 H H = 8 s i n ( 53.1 ) = 10 H = \frac 8 {sin(53.1)}=10 Now if we call the angle at 53.1 point E, then: B E = 10 \overline {BE}=10 A E = B E 2 A B 2 = 1 0 2 8 2 = 36 = 6 \overline {AE}=\sqrt {\overline {BE}^2 - \overline {AB}^2}=\sqrt{10^2-8^2}=\sqrt{36}=6 C E = 15 A E = 15 6 = 9 \overline{CE} = 15 - \overline{AE} = 15 - 6 = 9 B E C = 8 × 9 2 = 72 2 = 36 \triangle BEC=\frac{8\times 9} 2=\frac {72} 2 =\boxed {36} Therefore the area of the blue shade is: B C D + B E C = 34 + 36 = 70 \triangle BCD + \triangle BEC = 34 + 36 = 70 Thank you to everyone who attempted my puzzle!

Good One really,these are confusing triangles.Thanks K.K.GARG,India

Krishna Garg - 6 years, 8 months ago

I took tan(53.1)=8/AE instead of sin(53.1) That gives AE~ 6 So CE=15-AE=9 It saves some lines I guess!

Farzana Afroz - 6 years, 7 months ago

Log in to reply

Great idea! That definitely would have saved time! The main reason I used Sine was because people may be more familiar with Sine than Tangent.

Stewart Feasby - 6 years, 7 months ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...