#include <bits/stdc++.h>
using namespace std;
int n, q;
int value[300007];
vector<pair<int, int> > v[300007];
long long dp[300007];
long long up[300007];
int lvl[300007];
int LCA[300007][21];
long long prefix[300007];
void dfs_bot(int vertex, int prv) {
  int i;
  int sz = v[vertex].size();
  dp[vertex] = value[vertex];
  if (prv != -1) {
    for (i = 1; i < 21; i++) {
      LCA[vertex][i] = LCA[LCA[vertex][i - 1]][i - 1];
    }
  }
  for (i = 0; i < sz; i++) {
    if (v[vertex][i].first == prv) {
      continue;
    }
    lvl[v[vertex][i].first] = lvl[vertex] + 1;
    LCA[v[vertex][i].first][0] = vertex;
    dfs_bot(v[vertex][i].first, vertex);
    long long aux = dp[v[vertex][i].first] - 2 * v[vertex][i].second;
    if (aux < 0) {
      aux = 0;
    }
    dp[vertex] += aux;
  }
}
void dfs_top(int vertex, int prv, long long prv_edge) {
  up[vertex] = dp[vertex];
  if (prv != -1) {
    long long aux = up[vertex] + up[prv];
    aux -= 2 * prv_edge;
    aux -= max(dp[vertex] - 2 * prv_edge, 0LL);
    if (up[vertex] < aux) {
      up[vertex] = aux;
    }
  }
  int i;
  int sz = v[vertex].size();
  for (i = 0; i < sz; i++) {
    if (v[vertex][i].first == prv) {
      continue;
    }
    dfs_top(v[vertex][i].first, vertex, v[vertex][i].second);
  }
}
int get_lca(int x, int y) {
  int i;
  for (i = 21 - 1; i >= 0; i--) {
    if (lvl[x] - (1 << i) >= lvl[y]) {
      x = LCA[x][i];
    }
    if (lvl[y] - (1 << i) >= lvl[x]) {
      y = LCA[y][i];
    }
  }
  for (i = 21 - 1; i >= 0; i--) {
    if (LCA[x][i] != LCA[y][i]) {
      x = LCA[x][i];
      y = LCA[y][i];
    }
  }
  if (x != y) {
    x = LCA[x][0];
  }
  return x;
}
void calculate_prefixes(int vertex, int prv, int prv_edge) {
  int i;
  int sz = v[vertex].size();
  if (prv == -1) {
    prefix[vertex] = 0;
  } else {
    prefix[vertex] = prefix[prv] - prv_edge;
  }
  prefix[vertex] += dp[vertex];
  if (prv != -1) {
    long long aux = dp[vertex] - 2 * prv_edge;
    if (aux < 0) {
      aux = 0;
    }
    prefix[vertex] -= aux;
  }
  for (i = 0; i < sz; i++) {
    if (v[vertex][i].first == prv) {
      continue;
    }
    calculate_prefixes(v[vertex][i].first, vertex, v[vertex][i].second);
  }
}
void input() {
  scanf("%d%d", &n, &q);
  int i;
  for (i = 1; i <= n; i++) {
    scanf("%d", &value[i]);
  }
  for (i = 1; i < n; i++) {
    int x, y, z;
    scanf("%d%d%d", &x, &y, &z);
    v[x].push_back(make_pair(y, z));
    v[y].push_back(make_pair(x, z));
  }
}
void solve() {
  dfs_bot(1, -1);
  dfs_top(1, -1, 0);
  calculate_prefixes(1, -1, 0);
  while (q != 0) {
    q--;
    int x, y;
    scanf("%d%d", &x, &y);
    int u = get_lca(x, y);
    long long ans = up[u];
    ans += prefix[x] - prefix[u];
    ans += prefix[y] - prefix[u];
    printf("%I64d\n", ans);
  }
}
int main() {
  input();
  solve();
  return 0;
}
