Y3 symmetry homework help

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I've been trying to upload a picture of one of the shapes but I'm struggling to get it on here for some reason (would help as you may not know what I'm talking about)

Ds came home with symmetry homework. He has to complete the shape, some are easy (ish) but there are a couple where even I'm stumped and I've had to uses mirror on the dotted line to fathom out what the finished shape could be

I need to explain how to complete the shape without using a mirror but I haven't got a clue.

The shape has a line 1.7 cm across (top line) 2.2cm down and 4 cm (bottom line) there is a diagonal dotted line cutting through this half of the shape, Ds should then continue to draw the other half. Ds looked at it and thought it should continue into a rectangle shape but it doesn't because of the diagonal cut.

If you've followed me so far, well done.

Not sure I've got a clear idea of the shape, but if the diagonal line is the dotted one (line of symmetry) and the 1.7cm and 4cm lines are parallel to each other, would the completed shape be like an arrow? or a V?

A
|
|
|
__ B

So like this (imagine the dotted line a solid line) The cut through is diagonal from A to B. When you put a mirror to this line it flips up. I can't explain myself very well sorry.

I am pathetic at Maths btw.

Tell your ds to draw what he sees in the mirror line from A to B. Job done. Enjoy the rest of your Sunday.

Doesn't the line go at 90 degrees up from A and B making a kind of squarish heart shape.

So therefore it should "flip up".

I see what your ds means but if he folded his rectangle along the line of symmetry it wouldn't match. The finished shape is a sort of chevron pointing down to the right.

Yes, it looks like an arrow or square heart shape (good description )

We can see how the shape looks when you hold a mirror but how do you explain how this is achieved without a mirror?

Is there a grid to use for example?

Yes, like a chevron!

You could try graph paper maybe. If you cut out the shape and tilt it so the line of symmetry is vertical or horizontal it might give him a better idea on where the other half lies.

Thanks, Camolips.

Yes, I think we'll have to use graph paper but I'm sure he's expected to be able to 'see' the shape without.

Think I'll have to pop in to see the teacher. I'll also make a note to tell her which ones he struggled with.

I think some children can just see these easily, and others can't, and attempts to explain a method or system for getting the right answer never really work. The best things for children who can't see it, is to just do lots and lots of examples, using a mirror. Start with simple ones, then work up gradually. Maybe do some predictions first, imagining which one a part of it will go and seeing if you're right, etc., talking about it together. And definitely moving head/paper/objects etc so that the child is seeing it with the axis of symmetry vertical - we can perceive symmetry much, much better that way.

You can also do lots of the fun stuff with paint and folded paper, and looking at how the designs turn out, and/or looking for symmetry in real life

Thanks, Runaway.

Yes, Ds seems to have been a bit stumped by this. He did mention earlier in the week that he'd struggled a bit with symmetry in the lesson. He's quite able at Maths normally but he (and I) can't 'see' this.

I will do lots more practice with him as you've suggested and use various methods. He says that they haven't used a mirror in the classroom so I'm wondering which methods were used to explain.

Thanks everyone.

I would agree, some children ( and adults!) can just "see" symmetry and others can't -and it seems to have nothing to do with general mathematical ability. In fact some of my brightest mathematicians find shape and space generally difficult!
Changing the orientation sometimes helps, using tracing paper and "flipping it along the line of symmetry can also help as does folding along the line. If he struggles to "see" it, I would work on the manipulation aspects.

Would it help to rotate the paper slightly so that the line of symmetry is vertical?

Also, if it helps him to use a mirror I would just use one, even if they haven't in class.

My DD1 struggles with this.

This helps:

Turn the paper so the line of symmetry is vertical, and the half you have is on the left.
Then put a pencil in each hand.
Move the pencil along the line you have with the left hand, and mirror it with the right hand drawing on the paper. When mirroring, think whether you moving up or down, and away or towards the symmetry line.

Easier to do than say.

Thanks for all of your suggestions.

Worked on some of your suggestions tonight and he's getting there but still some work to do.

Will make a note in his homework book.

Try reflective symmetry game here: resources.woodlands-junior.kent.sch.uk/maths/shapes/coordinates.html#Symmetry

Look at the shape as a series of points and reflect each point by counting or measuring how far it is to mirror line hitting mirror line e at 90 degrees. Then count or measure the same distance on the other side. Finally join points up.