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When should I use the imperfect tense, and when the perfect tense?

The imperfect is used for: - description in the past (eg the door was red - la porte était rouge) - things that you used to do many times in the past (eg I used to go swimming - je nageais ) - interrupted ac...
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Answered by Sally W. • French tutor
3497 Views

What is the difference between reflection, refraction and diffraction?

These are all properties of waves and their definitions are useful to remember for exams. It can also be helpful to draw diagrams of each to help you to remember the difference. On the diagram it is useful t...
AK
Answered by Anna K. • Physics tutor
12782 Views

Expand and simplify 3(2x + 5) – 2(x – 4)

Firstly, to expand an equation like this, you must multiply the brackets by the number outside of the brackets. Make sure that you multiply every number inside the bracket by the number directly outside, and...
AK
Answered by Anna K. • Maths tutor
79697 Views

Explain the Chain Rule

The chain rule is used to differentiate composite functions, ie "a function of a function". In this case we have an outer function and an inner function. For example Differentiate f(g(x)). Here f i...
AC
Answered by Alex C. • Maths tutor
4700 Views

What is the angle between the position vectors a and b, where a = (6i - j + 3k) and b = (-4i + 2j + 10k)?

cos( AOB ) = a.b /(| a | x | b |) a.b = (6i - j + 3k) . (-4i + 2j + 10k) = (6 x -4) + (-1 x 2) + (3 x 10) = -24 + -2 + 30 = 4 (| a |)^2 = 6^2 + (-1)^2 + 3^2 = 36 + 1 + 9 = 46 -> | a | = 46^(1/2) (| b |)^2...
DH
Answered by David H. • Maths tutor
6761 Views