An applied problem of equation in grade one of junior high school According to the diagram, one triangle needs three matchsticks, and two triangles need five matchsticks. Let's build n triangles. How can you express the number of matchsticks needed by N triangles with the algebraic formula of N? Now there are 2009 matchsticks. How many such triangles can you build? 2100? (list the equation and solve it, without listing the process,

An applied problem of equation in grade one of junior high school According to the diagram, one triangle needs three matchsticks, and two triangles need five matchsticks. Let's build n triangles. How can you express the number of matchsticks needed by N triangles with the algebraic formula of N? Now there are 2009 matchsticks. How many such triangles can you build? 2100? (list the equation and solve it, without listing the process,

Building n triangles requires 3 + 2 (n-1) = 3 + 2n-2 = 2N-1 matchsticks
When there are 2009 matchsticks, that is to say, 2N-1 = 2009, n = 1005, so 2009 matchsticks can build 1005 triangles
Similarly, 2n + 1 = 21000, n = 10500.5, about 10500