Three quarter of a thousand

Geometry Level 1

csc ( 75 0 ) = ? \large \csc(750^\circ) = \ ?


The answer is 2.

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8 solutions

Siddharth Singh
Jun 16, 2015

csc ( 7 5 ) = 1 s i n ( 7 5 ) \csc(75^\circ)=\frac{1}{sin(75^\circ)} -(1)

sin ( 7 5 ) = s i n ( 4 5 ) c o s ( 3 0 ) + c o s ( 4 5 ) s i n ( 3 0 ) \sin(75^\circ)=sin(45^\circ)*cos(30^\circ)+cos(45^\circ)*sin(30^\circ)

we get sin ( 7 5 ) = 6 + 2 4 \sin(75^\circ)=\frac{\sqrt{6}+\sqrt{2}}{4}

from(1)

csc ( 7 5 ) = 4 6 + 2 \csc(75^\circ)=\frac{4}{\sqrt{6}+\sqrt{2}}

rationalizing 4 6 + 2 = 6 2 \frac{4}{\sqrt{6}+\sqrt{2}}=\sqrt{6}-\sqrt{2}

hence proved:

csc ( 7 5 ) = 6 2 \csc(75^\circ)=\sqrt{6}-\sqrt{2}

Hitesh Ar
Jun 16, 2015

cosec(2x360+30)

cosec30=2

Moderator note:

For clarity, you should mention that csc ( x ) \csc(x) has a period 36 0 360^\circ , so csc ( 75 0 ) = csc ( 75 0 2 × 36 0 ) = csc ( 3 0 ) = 1 sin ( 3 0 ) = 1 1 / 2 = 2 \csc(750^\circ) = \csc(750^\circ - 2\times 360^\circ) = \csc(30^\circ) = \frac1{\sin(30^\circ)}=\frac1{1/2} = 2 .

Bonus question : Prove that csc ( 7 5 ) = 6 2 \csc(75^\circ) = \sqrt6-\sqrt2 .

MahEnder BhojwAni
Jun 27, 2015

As we know.. Csc750° = csc30°

ans csc is the inverse of sin..

csc750°= csc30°= 1/sin30°

csc750°= csc30°= 2 ..

Yasmina Semsema
Jun 19, 2015

Csc=1/sin so we find sin (750) Sin750 =0.5 so csc (750) = 1/0.5 =2

Andy Velasco
Jun 17, 2015

750 degrees is the same as 720 degrees (2 full laps) and 30 degrees. We know from unit circle that the sin of 30 degrees is 1/2. For csc, just flip the fraction. Answer is 2.

Vivek Oza
Jul 15, 2015

Always keeping in the mind the phasor rotates with a period of 360 degrees. For ex. A minute hand in a clock ( assume it makes an angle ᶿ (theta) from position 12 in a clock ; when minute hand completes one rotation angle of 360 degrees. Similarly for two rotation it is 360 * 2=720 deg. ) So in this problem for any number greater than 360, reduce it to the form X=Number- 360*n ; where, n is an integer (1,2,3,......) in the above problem, x= 720 - 360 * 2; » x=30.

so finally csc(x)=1/sinx , sin(30)=1/2;

Ans. » csc(30)= 2

Anjali 1999
Jun 30, 2015

Cosec(750°)=cosec(720°+30°)=cosec30°=1/sin30°=2

Praveen Gupta
Jun 18, 2015

750-2*360=30 Cosec30=1/sin30=2 + with ASTC

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