a^2-b^2=(a+b)(a-b)
a^3+b^3=(a+b)(a^2-ab+b^2)
a^3-b^3=(a-b)(a^2+ab+b^2)
Ren Baqian was writing formulas on the blackboard when he suddenly left the classroom and looked toward the palace.
He felt an angry and murderous aura from the palace.
He was very familiar with this aura.
It was the empress.
She hadn't been this angry in a long time. Even people at the school could sense her aura. It was as if Mount Buzhou[1.Mount Buzhou: a mountain from Chinese legend] was going to collapse at any time and crush everyone to smithereens.
"Study this lesson yourselves!" Ren Baqian turned and told the students.
They were all crowded at the window and looking at the palace in shock. After that, Ren Baqian dashed straight for the palace.
