Pure Formulae

Question 1

Sin2x =

Answer 1

2sinxcosx

Question 2

Sin(a ± x) = …

Answer 2

SinaCosx ± CosaSinx

Question 3

Cos2x = … (all 3)

Answer 3

Cos²x - Sin²x
1 - 2Sin²x
2cos²x - 1

Question 4

Tan2x = …

Answer 4

2tanx / (1 - tan²x)

Question 5

Cos(a+x) = …

Answer 5

SinaSinx -/+ CosaCosx
(-/+ is flipped ±)

Question 6

For small angles, sinx ≈ …

Answer 6

Sinx ≈ x

Question 7

For small angles, tanx ≈ …?

Answer 7

Tanx ≈ x

Question 8

For small angles, cosx ≈ …?

Answer 8

1 - (x² / 2)

Question 9

The two AS Trig formulas.

Answer 9

Sin²x + Cos²x = 1
Tanx = sinx/cosx

Question 10

The three A2 Trig formulas.

Answer 10

Cotx = cosx/sinx
1 + tan²x = sec²x
1 + cot²x = cosec²x

Question 11

Cotx = … (reciprocal)

Answer 11

1 / tanx

Question 12

Cosecx = … (reciprocal)

Answer 12

1 / sinx

Question 13

Cosecx = … (reciprocal)

Answer 13

1 / sinx

Question 14

Secx = …? (Reciprocal)

Answer 14

1 / cosx

Question 15

Nth term for arithmetic series.

Answer 15

a + (n-1)d

Question 16

Sum of an arithmetic series (with last term)

Answer 16

(n/2)(a + l)

Question 17

Sum of arithmetic series. (Without last term)

Answer 17

(n/2)[2a+(n-1)d]

Question 18

Nth term of geometric sequence.

Answer 18

ar^(n-1)

Question 19

Sum of nth terms in geometric series.

Answer 19

[ar^(n-1)] / r-1
Check this?

Question 20

Sum of converging geometric series.

Answer 20

a / (1-r)