Saturday, March 29, 2014

2 + 2 = 5

When I was in first year of college, a senior who was preparing for a competitive exam asked me to help him with his maths. For each hour of tuition he would treat me to biryani, which I considered an excellent deal.

In our second lesson, I explained how to solve quadratic equations by factoring by inspection.

Then I derived for him the general solution for ax2 + bx + c = 0, the quadratic formula which in Indian textbooks is often called Sridhar Acharya's formula after the 9th century Indian mathematician who described a general method for solving quadratic equations:

I advised my friend that if a and c are integers with relatively few factors, factoring by inspection is quicker, so he should try it first before using the quadratic formula. He rejected this suggestion with an argument of such staggering irrationality and misplaced patriotic pride, that I could think of nothing to say in reply: "When there is a perfectly good method discovered by an Indian, why should I use another method?"

The incident came to mind because I noticed an amusing photo on the Guardian (online edition) front page today:
The teacher(?) is factoring a quadratic polynomial 2x2 + 5x + 2, but the expression in the second line is incorrect: (2x + 2)(x + 1) actually equals 2x2 + 4x + 2. The second line should read (2x + 1)(x + 2).

And yeah, there also should be a full-stop after 'charts'.

3 comments:

Tapobrata Mukhopadhyay said...

I think the equation beside it is also done wrongly. (Although it's difficult to read it).
Maybe she had actually called a student to the board and he did it all wrongly and she was pointing that out
That would explain the line she is drawing from under 3x and moving towards 1. (In a bid to graphically explain to the child how it is done.)

The Reluctant Rebel said...

I see you are just as annoying a teacher as you were a student (whatever the darwans at South Point say).

Sroyon said...

@Tapograta: Hmm, the other equation looks correct to me, but I admit it's hard to be sure.

@Saha: There was nothing annoying about my teaching, it was perfectly good advice!