20. Which of the following is not an identity? a) sin2 a+cos2 a = 1
b) sin a = tan a * cos a
c) 1 + cot2 a = csc2 a
d) 1 - sec2 a = tan2 a

Choice D)  1 - sec^2(a) = tan^2(a) is not an identity.

Explanation:

a) is the pythagorean trig identity assuming you meant to write sin^2(a)+cos^2(a) = 1

b) is a rewritten version of tan = sin/cos. You multiply both sides by cos(a).

c) is an identity that you can find through dividing everything in equation (a) by sin^2. I'm assuming you meant to put exponent symbols before each "2".

d) is not an identity. I recommend looking at a table or graph that compares the two sides as separate functions. You should see they are not the same. The actual identity should be sec^2(a) - 1 = tan^2(a). You divide both sides of equation (a) by cos^2 and do a bit of algebra to get it into this form.

d i think

step-by-step explanation:

54 kilometers per hour

step-by-step explanation:

according to rules:

1 km = 1000 meter

which means that 1 meter = 1/1000 km

1 hour = 3600 second [ as 1 hour = 60 min = 60 *60 seconds ]

which means that 1 second = 1/3600 hour

therefore, 1 kilometer/hour =

thus to convert 15 meter per second to kilometer per hour, we multiply 15 to 3.6 kilometer/hour.

15 meter/second=   which is the required answer.