equations to memorise

Question 1

when working out hcf from a prime factor tree, multiply..

Answer 1

shared factors

Question 2

when working out lcm from a prime factor tree, multiply..

Answer 2

everything

Question 3

quadratic formula

Answer 3

when ax²+bx+c=0

x = (-b ± √(b²-4ac)) / (2a)

Question 4

sine rule

Answer 4

a/sinA=b/sinB=c/sinC

Question 5

pythagoras’ theorem + when does it apply?

Answer 5

right angled triangles
a²+b²=c²
where c=hypotenuse

Question 6

percentage change

Answer 6

change in value/ origial value x 100
(percentage decrease will be negative)

Question 7

cosine rule (finding side length)

Answer 7

a²=b²+c²-2bc x cosA

Question 8

cosine rule (finding angle)

Answer 8

cosA = b²+c²-a²/2bc

Question 9

volume of a cone

Answer 9

1/3 x pi x r² x h

Question 10

surface area of a cone

Answer 10

pi x r² + pi x r x l

Question 11

volume of a cylinder

Answer 11

pi x r² x h

Question 12

surface area of a cylinder

Answer 12

2( pi x r x h) + 2( pi x r²)

Question 13

if a:b=c:d…

Answer 13

c/a = d/b

Question 14

equation of a straight line

Answer 14

y-y1 = m(x-x1)

Question 15

proportional

Answer 15

y=kx

Question 16

inverse proportional

Answer 16

y=k/x

Question 17

area of a triangle (2)

Answer 17

A = ½bh
A=½ ab x sinC

Question 18

main pythagorean triangles (3)

Answer 18

3, 4, 5
5, 12, 13
7, 24, 25

Question 19

finding diagonal of a cuboid 1 step method

Answer 19

square root (x² + y² + z²)

Question 20

sin60

Answer 20

√3/ 2

Question 21

cos60

Answer 21

½

Question 22

tan60

Answer 22

√3

Question 23

sin30

Answer 23

½

Question 24

cos30

Answer 24

√3/2

Question 25

tan30

Answer 25

1/ √3

Question 26

SOH CAH TOA + when does it apply

Answer 26

right angled triangles ONLY sin = opposite/ hypotenuse cosine = adjacent/ hypotenuse tangent = opposite/adjacent