Su Dongpo, a great poet in the Song Dynasty, is not only good at poetry, but also likes painting. Once, after he painted a picture of Birds Returning to the Nest, his poet friend Wen Lunxu wrote such a "mathematical poem": "One after another, three four five six seven eight. There are many phoenix birds, pecking out thousands of stones in the world. " Analyzing this poem, it is not difficult to see the following "mathematical meaning", that is, the first sentence contains the formula "1+1= 2"; The second sentence contains the formula "3× 4+5× 6+7× 8 = 98". The sum of the two formulas is "100", which coincides with the "hundred birds" in the picture.